Rich, since i have the same top off as you i can offer this advice. Put the topoff hose to pump righ tinto the overflow. That's how i have mine and never had a problem. Just make sure it is not submerged. I made a mistake one time by placing it in the sump. Since the reservoir had a higher water level, the water continued to siphon even though the hose was not submerged in the sump. These are the little things we forget.

The pump itself i believe pumps up to 9ft. Not bad for a little pump. So you should have no problems running it up to the overflow. HTH